1. Field of the Invention
The present invention relates to an image processing device for processing images used for diagnosing atrophic gastritis and a method for operating an endoscope system.
2. Description Related to the Prior Art
Diagnoses using endoscope systems have been widely performed in medical fields. The endoscope system comprises a light source device, an electronic endoscope, and a processor device. Due to high resolution achieved by a high-definition imaging system such as an imaging element, which is to be incorporated in the endoscope, with high sensibility and a high number of pixels, recent models of the endoscope systems display high resolution images that surpass the current image quality. Owing to this, fine blood vessels and a small lesion in mucosa displayed look extremely real.
Such high-definition imaging clarifies the shape and the size of a lesion, facilitating the detection of the lesion. However, a doctor finds a lesion based not only on the shape and the size of the lesion but also on a slight difference in color between portions of mucosa. For example, a slightly reddish area that is slightly different in color from the mucosa is detected as a lesion in its early stage. The slightly reddish area may be overlooked only by increasing the resolution with the use of the high-definition imaging.
In Japanese Patent No. 3228627, a color enhancement process is performed to enhance the redness of a reddish area and the whiteness of a white area in an image to prominently display a border between a normal portion and a lesion. The color enhancement process enables finding a lesion which cannot be detected only by using the high-definition imaging.
In recent years, a stomach lesion such as stomach cancer has been detected based on a state of atrophic gastritis. The relationship between the atrophic gastritis and the stomach lesion, which will be described below, is used for the detection. As illustrated in a part (A) of FIG. 30, a surface mucosal layer of normal gastric mucosal structure has certain thickness, so that the mucosal layer absorbs or reflects most of the light. For this reason, the blood vessels in the normal submucosal layer are hardly observed in an endoscopic image as illustrated in a part (B) of FIG. 30.
As illustrated in a part (A) of FIG. 31, in the case of gastric mucosal structure in an advanced stage of the atrophic gastritis, the mucosal layer is thin due to decrease in gastric glandular cells. Changes in internal structure of the gastric mucosa with the progress of the atrophic gastritis exhibit the following features (A) and (B) in an endoscopic image.
(A) The whitish color of muscularis mucosae is seen through the atrophic mucosa, so that the atrophic mucosal portion shows fading of color as compared with the color of the normal portion.
(B) The blood vessels in the submucosal layer are seen through the mucosal layer in the atrophic mucosal portion as the thickness of the mucosal layer decreases with the progress of the atrophy (see a part (B) of FIG. 31).
In diagnosing a gastric lesion based on the atrophic gastritis, the above-described two features (A) and (B) are used for determining staging of atrophy and a border between the normal portion and the portion with the gastritis.
In a case where the atrophy is in its advanced stage (for example, in a case where the atrophy is included in the group C or the group D in the ABC screening), the above-described features (A) and (B) are clearly observed in the endoscopic image. However, in a case where the atrophy is in an intermediate stage (for example, in a case where the atrophy is included in the group B or the group C in the ABC screening), there is little difference between the atrophic portion and the normal portion in the endoscopic image, so that it may be difficult to determine the staging of atrophy and the border between the normal portion and the portion with the gastritis. It is required to display the two features (A) and (B) clearly in the endoscopic image to clarify the border between the normal portion and the portion with the gastritis.
The method described in the Japanese Patent No. 3228627 may be applied to achieve the above. However, the method described in the Japanese Patent No. 3228627 enhances only the redness of a reddish area in an image and cannot enhance the changes in color of mucosa with the progress of the atrophy of the stomach and cannot enhance and display the blood vessels that are located beneath the mucosa and seen through the mucosa as the atrophy progresses.